The effects of ascorbic acid include the inhibition of lipid peroxidation, acceleration of collagen formation, retardation of melanin formation, enhancement of immune functions and the like. For these purposes, ascorbic acid has hitherto been used in the fields of medical preparations, agricultural chemicals, animal drugs, foods, feeds, cosmetic preparations and the like. However, ascorbic acid has poor aging stability and poor liposolubility. Accordingly, the cumulative amount thereof in cells after permeating through the cell membrane is limited, and the physiological actions of vitamin C cannot be achieved to a satisfactory extent.
To cope with this, various derivatives have been proposed, where the hydroxyl group present in the enediol part at the 2- or 3-position, which is easily oxidized, is transformed into a phosphoric acid ester (as described, for example, in JP-B-52-1819 (the term "JP-B" as used herein means an "examined Japanese patent publication") and JP-A-02-279690 (the term "JP-A" as used herein means an "unexamined published Japanese patent application")) so as to improve stability, or is acylated with a fatty acid to thereby improve liposolubility (as described, for example, in JP-A-59-170085).
Of the conventional ascorbic acid derivatives, compounds having satisfactorily improved stability (for example, magnesium L-ascorbic acid 2-phosphate) still lack adequate liposolubility.
JP-A-58-222078 proposes a 6-O-alkanoyl-ascorbic acid-2- or -3-phosphoric acid ester as a novel compound having increased stability and an appropriate solubility in lipoid. The alkanoyl group thereof has less than eleven carbon atoms, and only a pivaloyl group is disclosed as an example thereof. The compound of the present invention cannot be obtained by the production process disclosed in JP-A-58-222078. Furthermore, the novel compound disclosed therein does not have both sufficiently improved stability and liposolubility.
JP-A-61-152613 describes a cosmetic material containing a 6-O-higher acylascorbic acid-2-phosphoric acid ester. In this patent publication: first, transformation into a sulfuric acid ester but not into a phosphoric acid ester is described; second, the ascorbic acid derivative thus obtained is not identified; and third, the results of the working examples thereof are closely similar to those of the working examples of JP-A-61-151107 where the same experiment is performed except for using a 6-O-higher acylascorbic acid-2-sulfuric acid ester. Taking these facts into account, it can be concluded that the ascorbic acid derivative used in JP-A-51-152613 neither discloses nor suggests a 6-O-higher acylascorbic acid-2-phosphate.
EP0339486and German Patent Publication DE4000397A1 propose compounds such as 6-O-octadecanoyl-2-(O*,O*-diethyl-phosphoryl)-ascorbic acid. However, these compounds are intended to capture active oxygen, and the ethyl group or the like remains bonded to the phosphoric acid group. Therefore, these compounds have deficient stability, are hardly susceptible to the action of phosphatase, and are not easily biotransformed into ascorbic acid.
As described in the foregoing, various L-ascorbic acid derivatives have been proposed, however, an ascorbic acid derivative having sufficiently high stability, appropriate liposolubility, and which is capable of satisfactorily attaining an increased ascorbic acid intracellular cumulative amount has not yet been obtained.